Operational status (ON/OFF, power consumption, and the like) of an individual electrical apparatus can be simply recognized by mounting a measuring device to a power supply of each apparatus. However, there is a problem of a burden imposed on a user due to labor and time required for the installation thereof or a problem of the required cost of the measuring device.
A method disclosed in Patent Document 1 can be given as a means for solving such a problem. In this method, an operational status of an individual electrical apparatus is inferred using information regarding a voltage and a current which are measured in the vicinity of a power feed inlet. According to this method, it is possible to reduce a burden on a user and cost, as compared to a method of mounting a power measuring device to every apparatus.